Hi again Aley,
You say you found Walter in 1851 and 1861. What was his birthplace on those censuses?
Given that your Walter ROSS married in Petty in 1848, there is a possibly interesting entry for a Walter ROSS in 1841 on FreeCEN.
Balenldrich, Petty/Nairn, Inverness-shire
SCT1841/106/ED 1/Folio 7/Page 3
ROSS Walter, 30, Farmer, born Outside Census County
FALCONAR Margreat, 65, b Nairn
ROSS Margreat, 10, Female Servant, b OUC
MCKAY Alexr, 15, Ag Labourer, b Nairn
Thinking that Margreat FALCONAR might well be the mother of this Walter, I searched for the birth of a Walter ROSS mother Margreat FALCONAR.
Walter ROSS, b 2 Feb, bap 12 Feb 1807, Abernethy & Kincardine, Moray, parents William ROSS & Margaret FALCONER.
Unfortunately, the only marriage I can find of a William ROSS & a Margaret FALCONER is in 1824 (

) in Dyke, Morayshire.
The only births in the IGI to a William ROSS & a Margaret FALCONER are Charlotte ROSE bap 1795 in Nairn, Nairn-shire (this is an LDS submission) then, the following extracted entries all in Abernethy & Kincardine, Moray-shire - John ROSS b 1797, Margret ROSE b 1799 and Walter ROSS b 1807 (and the following, with mother's name as Margaret ROSS, may also be theirs - William ROSS b 1801).
It will be interesting to hear what Walter's birthplace was in 1851 and 1861, and what the Petty death cert says (re name of wife and names of parents) if you download it.
JAP